Telephone trunking system



`.T. G. MARTIN. TELEPHONE TRUNKING SYSTEM.

Reissued Oct.. 5i APPLlATlON F`lLED Ml-\Y28,191?- 5 SHEETS-SHEET l.

, N l Qllmhllh@ T. G. MARTIN.

`TELEPHONIE TRUNKING SYSTEM.

APPLICATION FILED Mmes, |911.

Reissued 00T. 5, 1920. 14,954.

5 SHEETS-SHEET 2. f

l Ihm-lh TKG. MARTIN.r TELEPHONEIRUNKIN SYSTEM. APPLICATION FILED MAY 28. 19H'.

Reissned oct. 5, 1920.

5 SHEETS-SHEET 4.

N llll Imre T. G. MARTIN.

TELEPHONE TRUNKING SYSTEM.

lessued Oct' 5 APPLICATION FILED MAY 28,l I9IZ. l

5 SHEETS-SHEET 5.

- JmL/'Erinn- YZb/:Z E. Mrm,

UNITED fsTArEsvrATENT TALBOT Gr. MARTIN, OF CHICAGO, ILLINOIS, ASSIGNOR, :BYv ASSIGNMENTS, TO AUTOMATIC ELECTRIC COMPANY, A CORPORATION OF. ILLINOIS.

TELEPHONE TRUNKING SYSTEM.

Specification of Ressued Letters Patent. Reissued 001;. 5,' 1920.

original No. 1,201,600, dated october 17, 191s, serial No. 394,984, mea september 2s, 1907. plint-,ation for reissue filed May 28, 1917. Serial No. 171,604.

T 0 all whom tf/nay concern,

Be it known that I, TALBOT GuMARTIN, a citizen of the United States of America, and resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in Telephone Trunking Systems, of which the following is a specification.

My invention relates to telephone systems in general, but more particularly to automatic or semi-automatic telephone exchange systems, and especially to systems in which automatic or semi-automatic Atrunking service may be required between two or more of the exchanges or central stations comprised in such system.

In certain respects my present invention isin the nature of an improvement on my f Patent No. 1,109,650, granted September 1,

1914, for improvement in Telephone Exchange Systems, inasmuch as it involves separate and distinct means yfor automatically trunk'ing in opposite directionsover a trunk-line and it 'is also in the nature of an improvement on the s stemddisclosed in the patent to VVilsoIi L. ampbell for improvement in telephone systems, No. 1,181,092,

. granted April 25, 1916,'inasmuch as I have herein disclosed animproved arrangement of rotary connectorsthat is to say, connectors which are adapted to rotate and automatically select idle trunk-lines, the rotary y or automatic trunk-selecting feature being `limited or confined to a certain level, and the other levels thereof being employed for ordinar service-*that istosay, forlcomplet- -ing t e final connections directly with the lines of .the called subscribers.

My` present. invention, however, contemplates broadly a combined connector and re- I -peater,fwith provisions for bringing the repeater mechanism into playonly when the connector .is operated at a certain level; and

' it also `contemplates broadly an automatic connector which is rotary ortrunk-selecting in characterat' a certain level only, and

which at this level is also Aadapted to have its line relays serve as part of the mechan'ism for then repeating or relaying switchoperating impulses over selected idle trunk-line.

As herein disclosed, my present invention and improvements are embodled 1n a system comprising al main automatic exchange and a branch automatic exchange connected toto ycall each other automatically;

ment of the branch exchange including subcall any subscriber at the main the automatically olirlcs.

cluding first and second selectors and cond nectors for enabling the subscribers thereof the equipscribers non-numerical tr'unking switches vand connectors, without any intermediate selectors, whereby' the subscribers thereof can call each otherautomatically. vFurthermore, as herein disclosed, there are two-way trunk-lines between the two exchanges, each trunk-line terminating ina first-selector and a repeater at the main exchange, as well as -in second-selector bank terminals ,and at-the branch exchange each o-f said trunk-lines terminates 1n a nonnumerlcal trunking switch, as well as in multiple terminals of A the connectors of this exchange. The said connectors of the branch exchange are adaptedl for use in giving ordinaryfservice between the subscribers thereof, and are also adapted, when raised to a certain level, to

rotate automatically and thereby automatically selectan idle trunk leading to the main exchange; `and these connectors which are, so to speak, rotary or trunk-selecting when operated at a certain level, are also adapted `to serve as repeaters, both the trunkselecting and repeating functions of these connectors being brought about, for-example, by raising any connector to the tenth level, all other levels of the bank terminals of the connectors being reserved for ordinary service-that is to say, formaking the final connections directly with the lines of called slib-` scribers.

With such arrangement any subscriber at the branch exchange can call any other subscriber thereof, and can-also automatically exchange, inasmuch as the connector-which idle trunk-line will then serve as a repeater for controllingthe iirst-'selector at the other end of saidvtrunk-line, as well as for controlling the second-selector and ordinary 'Connector necessarily brought into use in extending the connection to'and finding the line of the called subscriber at the main e'xchange. Also, with this arrangement any subscriber of the main exchange can call any other subscriber thereof, and'can also automatically call any subscriber at the branch exchange, as by raising the second-selector at the main exchange to a certain level the tion.

calling subscriber thereof can obtain connection with the repeater of an idle trunk-line leading to the branch exchange, and said repeater can then be employed for controlling the non-numerical trunking switch at the other end of the said trunk-line, as well as for ,controlling the connector necessarily brought into use at the branch exchange for completing connection to and nding the line of the called subscriber thereof. Means are provided,l as will hereinafter more fully appear, whereby when one of said trunklines is used in one direction, no subscriber can interfere with such use by attempting to use it in the same direction, or by attempting to seize it for use in the opposite direc- In this way I provide a system in which automatic service is provided between all of the subscribers thereof, and in which the connectors of a small branch exchange may be employed for automatically trunking a calling'subscriber thereof to the mainy exchange, and forthen controlling whatever automatic apparatus is necessary' in com-l pleting the connection to the line of the Y called subscriber at the main exchange; and,

ing connection with repeaters and trunky lines leading to the branch exchange.

as explained,-this arrangement permits the A subscribers of the main'exchange to use the first, and second selectors thereof for obtain- The nature and advantages of my invention will, however, hereinafter more fully appear. l

In the accompanying drawings Figure 1 represents diagrammatically a sub-central or private branch exchange in which the substation A is shown as having operated its line switch C" and the connector H to establish connection with the substation A', which latter is allotted to the line switch C', in a system embodying thevv principles of my invention. In Fig. 2 there is shown diagrammatically a central station switching apparatus in connection with which I have elected to explain my invention. The firstselector switches E and E are of the type disclosed in United States Patent No. 815,- 321, granted March 13,l 1906, to Keith, Erickson and Erickson,l while the secondselector F is a modified form of the selector shown in said patent. The connector switch shown at I is of the general type master switch D. 5 is a detail view of l private branch or sub-central exchange, andthe subscribers equipment at sub-station A3 of the main or central exchange.

The substations are all alike and may be of any suitable or approved type. /The substation A, for example, comprises a receiver 2, a switch-hook 3 for controlling the substation circuits, which controlling operations are accomplished through the medium of any suitable means, such as the cam-arms 4, 5` and 6. As the switch-hook is lowered the cam-arm 4 momentarily presses the release springs 7,8 and 9 into engagement, whereby the substation line conductors may be grounded simultaneously, if the springs 18 and 19 are in contact, for the purpose of releasing the switching apparatus at the central station. When the switch-hook is down the. cam arm 5 engages the spring 10, thereby bringing the ringer 11 in series with the condenser 12 across the line.

Furthermore, when the switch-hook is down the said cam-arm 5 disengages the springs 13 and 14, thus breaking the local circuit which includes in series the primary winding 15, transmitter 16 and local battery 17.

The substation ground circuit is normally 'broken between the ground springs 18 and 'secured to the shaft 25, together with the locking dog 26. Furthermore, there is .Y locking cam 27 that locks the dog 26 while the receiver is on the switch-hook to prevent a rotation of the dial. For operating the impulse springs 23 and 24 the substation is provided with an impulse wheel 28 that is secured to the shaft, which impulse wheel carries on its periphery the so-called Vertical impulse teeth 29 and one rotary impulse tooth 30. The said impulse teeth are so arranged that when the dial is drawn down the impulse spring 23 is not carried into contact with the ground post 20, but only as the dial returns, whereby the vertical impulse spring 23 is pressed onto the said ground post 20 by one or more of the vertical impulse teeth, and after the latter I the rotary impulse spring 24.. In this operation the subscribers vertical line conductor 31 is first given a number of ground impulses, and then the rotary line conductor 32 is given Yone ground impulse. It will be seen that the construction is such that as long as the dial is out of normal position the dog 26 permits the primary circuit springs 33 and 34 to separate, thus preventing the impulses that are delivered to either line conductor from passing to the other. The vertical impulse'spring 23 is provided with an oblique projection or lug 39 (see Figs. 6 to 12,.inclusive) on the under side of which the vertical impulse teeth 29 are adapted to engage for intermittently'driving the spring 23 onto-the ground post 20. The rotary impulse spring 24 is provided with somewhat similar mechanism for driving the said rotary spring onto the ground post once when the dial is rotated in one direction, and once when rotated in the opposite direction. The said rotary impulse spring 24 has on its under side a V-shapedl member 40 having .two sides 'c and d, and there is, in addition, an auxiliary spring 41 which .works in conjunction with the said V-shaped member. As shown more clearly in Fig. 6, the auxiliary spring 41 is provided with a lower curved part e having the rearsection 42 curving out'- wardly, as shown in Figs. 7, 8, 9, 10, 11 and 12. The front section 43 of said member e is designed to fall just behind the apex of the V-shaped member 40, so that the rotary impulse tooth 30, when moved in the direction indicated by the arro-w in Fig. 7,

will pass onto the curved member e, thus pressing the rotary impulse spring 24 onto the ground post 2Q for a comparatively long time, as shown in Fig. 8, thus sending'a comparatively long impulse to the line.

As the impulse wheel advances, the vertical impulse teeth 29 approach the lug 39 of the vertical impulse spring 23y (Fig. 8), and eventually the iirst tooth f that meets the lug 39 clears the said* lug, as shown in Fig. 9. but not until after the rotary impulse tooth 30 clears the curved member e. As the impulse wheel continues to dvance inthe direction of the'arrow (Fig. 9), the succeeding impulse teeth 29 will clear the projection 39,

as shown in Fig. 10. Then when the impulse Wheel isreleased, first the 'vertical impulse spring 23 is carried into engagement with the ground post 2() bythe vertical impulse teeth previously cleared, as indicated in Fig. 11; and as the impulse wheel nears its normal position the 'rotary 'impulse tooth 30.

passes underl the curved member .e of the auxiliary spring 41 (Fig. 12), engaging the V-shaped member 40directly and ,for a short time only, sending the ordinary impulse to the line 32 through the medium of the rotary impulse spring 24, after which the said member 40 is cleared or disengaged, as shown in Fig. 7. The operations as thus described are y repeated each time that the dial is operated,`

finger-hole which the subscriber selects thereon. The means whereby the subscriber may signal the calledv subscriber comprises the push-button spring 35 which normally engages the contact point 36; but when the button 37 is pressed the spring 35 engages the Contact point 38, whereby the vertical line 4conductor 31 may be grounded. As shown in Fig. 4, the individual switch comprises a plunger 44, plunger arm/45, bridgecut-oli relay 46, trip magnet 47 yfand switchrelease magnet 48, all of which are built about a switch-base or frame (not shown) of any suitable or approved design.v The said switch-release magnetis provided with an armature 49 that is pivoted on a pin 50 which rises from the base of the switch. The said armature carries pivotally secured on its venol a second armature 51 that is controlled by the tripv magnet 47. The pin 52 about which the armature 51 oscillates is carried on the end of the armature 49. Thel ',minals, usually ten in number, only one of which 4is shown at Q in Fig. 4. As shown, the said terminal Q is turned from its true position with respect to the swing of the plunger l44, and the bushing 62 is correspondingly turned, all for the purpose of making the illustration clearer. The ter minal Q comprises the springs 63 and 64, 65 and 66, 67 and 68, and 69 and 70. The said springs are normally disconnected from each other, but are driven into contact in the above-mentioned order when the plunger 44 operates. When the plunger 44-is in locked engagement with the plunger shaft 60, the notch 61 is in engagement with the flange or `web of the shaft 60, and when in sliding entracted against the magnet cores. -When the armature 51 lis attracted the .catch 56 slides out of contact with the end 57 of the plunger arm '45, and the said plunger arm 45, owing 'to the tension of the spring 58, moves about the pin 54 and thrusts the plunger 44 into the bank terminal Q (shown in Fig. 4), and when the trip magnet again denergizes, the trip armature 51 falls against the end of the plunger arm 45.

The switchy is restored when. the release magnet 48 becomes energized, whereby the armature 49 is arranged, and accordingly the trip armature 51 is moved upwardly until the catch 56 slides overl the end 57; then when the release magnet 48 becomes dener gized the armature 49 returns to normalposition by the action of the spring 58, since the plate 56 is now' locked on top of t-he plate 57, and the armature 49 remains at rest against the stop 55. Furthermore, since the plunger arm 45 is now in engagement with the armature 51, the said plunger arm is also moved about the pin54, whereby the plunger 44 is moved from the terminal Q. Also,

since the plunger shaft has advanced one I step, the hub 59 of the plunger 44 comes to rest in the' position shown by 4the dotted line in Fig. 4, in sliding engagement with the plunger shaft 60; and as the said plunger shaft advances each time an idle trunk is seized, the plunger 44 is not advanced, but

' remains in this position opposite the trunk terminal from whichit has just disengaged, y

From thence on the plunger 44 is carried by the shaft 60 until it is' again released when another call is made. But if, after the plunger is released, and before the shaft 60- rei turns Ato pick up said plunger, the switch C is again operated, the plunger l44 again engages the same terminal Q., The y master switch D, which may be of any suitable or approved type, is provided for operating the plunger shaft 60, and for controlling certain circuits that will be disclosed hereinafter. It comprises the following details: A motor magnet 71 for operating the ratchet wheel 72, which latter is designed for operating the plunger shaft 60, and a differential relay 73 for controlling lthe energizing circuit of the motor magnet 71. The said master switch also has a bank O comprising a plurality of individual contact` segments a,

adapted tov successively engage the pins 77 78, 79 and 80 upon the said ratchet wheel 72. The motor magnet 71 is provided with an armature 81 upon the end of which there is suitably secured a pawl 82. Each time thatl the said magnet is energized the pawl 82 engages the ratchet wheel 72, advancing the latter one step. It will be seen, therefore,

that as the ratchet wheel 72 advances, the

wiper 75 advances step by step from right to left, and when the pin 77, for instance, clears the cam 76 the retr'acting spring 83 restores the wiper 75 to its first position at the right of the bank O and in engagement with the first segment 84. The said motor magnet 71 is provided with a couple of interrupter springs 85 and 86 that are included in the energizing circuit of the said motor magnet, which energizing circuit also comprises thesprings 87 and 88 controlled by the differential relay 73. Therefore, whenever the differential relay 73 is energized the springs 87 and 88 are pressed into contact, and the motor magnet 71 operates step by step as long as the differential relay 73 remains energized. Furthermore, it is assumed that the terminal Q ofthe line switch C is the rst terminal of the line switch bank. While in normal locked engagement with the shaft60 the plunger 44 is retained in front of said terminal by the plunger shaft 60 as long as the master switch wiper 75 is in engagement with the bank segment 84; but as the motor magnet 71 advances the wiper 75 onto the second segment 89, the said plunger and all idle plungers similarly engaging the shaft 60 are carriedopposite the next terminal of the line switch bank. The master switch bank O (Fig. 5) comprisesthe individual segments a separated from the common segment 74 by the insulating strip 1.16.

It will be seen that after thewiper 75 passes over the segments Vfrom right to left and` engages the last segment 117, then on the next step the wiper 75 passes from the yextreme left contact 117 to the contact 84 on the extreme right; but in passing from this extreme positionto the other the upper part of the w1per 75 slides on the insulated meml ber 118. This provision isv made in order that the individual segmentsa may not be brought into contact with the common segments 74, whereby some interference with the successful operations of the master switch might be experienced. It should be noted that in each switch bank all of the springs 63 are permanently connected and may be made of one common piece. The springs 64, however, are individualthat is, there is one separate and distinct spring for every terminal Q, there being ten in the bank. The springs 65, 67, 68 and 6,9, like the springs 63, are also common, and the springs 66 and 70, like the springs 64, are individual. -For every bank terminal Q there is a trunk-line of three conductors 90,

91 and 92 leading to a connector switch; and there is also a normal trunkeline comprising the conductors 93, 94 and 95 leading to the connector switch banks. The subscribers line conductors 31 and 32 terminate in thev springs 63 and 65 which, as hasbeen stated, are common springs. When the subscriber operates the line switch C, and the plunger 44 engages the terminal Q, the subscribers line' conductors 31 and 32 are extendedto the vertical and rotary trunk conductors 90 and 91,-thence to the connector switch H.

The connector switch H is an improved form of the connector switch described in United States Patent No. 815,176.l For instance, the connector switch shaft carries the line wipers 96 and 97 and the private wiper 98. `The connector switch is also controlled by the calling subscriber through the medium of the vertical and rotary line relays 99 and 100. 'The vertical line relay 99 vdirectly controls the vertical magnet 101 and also the rotary magnet 102. The function of the vertical magnet 101 is to give the shaft and shaft wipers a vertical motion,

" and the rotary magnet; 102 imparts to the densers 110 and 111 the connector circuit shaft and shaft wipers a rotary or circular motion. The rotary line relay 100 controls the private magnet 103,l which latter, under certain conditions, controls in turn the vertical and rotary magnets Y101 and 102, the

r release magnet 104, and also the side switch wipers 105, 106, 107, 108 and 109. The side switch of the connector, like the side switch of the selector, has a normal or first posi? tion, a second position and a third position.

The release magnet 104 is also controlledby the vertical and rotary line relays 99 and 100 conjointly. By the use of the conis divided into two sections. The relay 112 is provided lforbridging the ringer generator K across the terminals of the called line. The relay 113, upon energizing, operates to disconnect the vertical. and rotary line relay springs 196 and 207, respectively, from the side switch wiper 107` and private magnet 103, and to connectthem instead to the .shaft wipers 96 and 97, whereby the succeed.

ing impulses from the connector vertical and rotary line relays are repeated to the conductors with which the wipers may 'be' in contact. Furthermore,`I it should be noted that the release mechanism of the connector lated.

H operates like that of the selector switch disclosed-in said selector-patent, instead yof like` that of the connector described in said connector patent-that is, the release of the switch is accomplished when the release magnet` `denergizes,' instead of when the magnet' energiZes,-as` is usually thecase in connector switches.`

In vorder toclearly describe the operation of the connector H, certain of the bank contacts of this connector are shown, which are as follows: .The bank contacts with which the wipers 96, 97 and 98 are shown in engagement are the tenth set of contacts loflthe second level, while the remaining bank contacts showny in connection with' said wipers 9 6, 97 and 98, but a littleabove them,

are the first, second, third and fourth set of bank contacts of the tenth level. Of these sets in the tenth level the first private bank 854 contact 210 is shown grounded, while the fourth rivate bank contact is shown insuhe selectors E, E and E2 shown in Figs. 2 and 3 areof the type disclosed in said selector patent. The selector switch E 90 is provided with a vertical magnet 127 and a rotary magnet 128,a release magnet 130 and a private magnet 129. The said private magnet 129, Aof course., controls the side switch wipers 131, 132, 133 and 134, the said 95' private magnet also controls theA circuit of the vertical magnet 127 in the usual manner,

by means of the springs 135 and 136, and also of the release magnet 130 through the springs and A1'37. The vertical move- 100l ment of the switch-shaft, and, therefore, of the wipers 138, 139 and 140, is controlled by the vertical magnet 127, while the rotary movement is controllediby the rotary magnet 128, the rotary magnet circuit being pro- 105 vided with the usual interrupter springs 141. The operative magnets of the switch are` of course, Ycontrolled by the subscriber through the use of the vertical and rotary line relays 142 and 143, as is well known. 110 Said relays have under Ytheir control the usual springs 144, 145 and 146. By means of the back-release relay 147 the release of the switch E is brought about after the side switch has ypassed to third position. 'Each 115 selector switch in thisA system is provided with line and private banks. The contacts vof each line bank are adapted to be engaged by corresponding line wipers such as thewnn.;

155. The modication is as follows: The line relays 148 and 149, as shown, control the socalled trunk-release springs 156 and 157, the former being connected with the trunk-release conductor 158 and the latter with the release magnet 154. The private magnet 155 in this switch F, unlike the selector E,

is not provided with the usual spring that is 343, 344 and 246 allotted to the selector E i (Fig. 2), these conductors are omitted. The usual shaft wipers'159, 160 and 161 are provided for engaging the bank contacts.

The connector switch I may also be of any suitable or approved type, and, as shown, is of the type described in said connector patent.l The connector switch shaft (not shown), like the first-selector switch shaft, carries the wipers 162, 163 and 164. The connector-switch is also controlled by the calling subscriber through the medium of the vertical and rotary line relays 165 and 166. The vertical line relay 165 directly controls the vertical magnet 167 and also the rotary magnet 168. The purpose of the vertical magnet 167 is to give the shaft and shaft wipers their vertical motion, and the rotary magnet 168 imparts to the shaft and shaft wipers `a. rotary or circular motion.

The rotary line relay 166 controls the private magnet 169 which, under certain conditions, in turn controls the vertical and rotary magnets 167 and 168, release magnet 17 0, and also the side switch wipers 171, 172, 173 and 174. The side switch .of the connector, like the side switch of the first-selector, has a normal or first position, a second position and a third. position. To release magnet 170 is also controlled by the vertical and rotary line relays 165 and 166 acting conjointly. This magnet 170 may also be energized through the medium of the backbridge relays 175 and 176 by the calledsubscriber if the calling subscriber does not bring about the release of the connector switch. The ringer relay 177, as usual, provides the means whereby the ringer generator M may be bridged across the line of the called substation. The central station or exchange is equipped with busy-signaling apparatus of any suitable design, comprising an interrupter in series with thel primary winding of an induction-coil, as shown at N, whereby a busy-signaling current is induced in the secondary winding 178 of the said coil.

Y second-selector switch. The relay 184, upon energizing, operates to establish a guarding potential at the second-selector banks to protect the repeater from being seized when the trunk-line to which the repeater J is allotted is engaged by a subscriber calling into the main exchange from the branch exchange.

A clear-er understanding of the operation of my improved system may be obtained by considering its action when one subscriber calls another. Assume, for example, that the subscriber at substation A (Fig. 1) desires to call some subscriber at substation A3, #2220 (Fig. 3), which is` allotted to the main exchange represented in Fig. 2. Since the trunk-lines from the sub-central office to the main-central office are, in this case, arranged to lead off from the tenth level of the connector bank, then when a main exchange connection is desired by a sub-exchange subscriber the subscriber must Y'first call naught on his dial. To call naught the subscriber at substation A operates the calling, device in the well-known manner corresponding to the digit naught. The preliminary impulse for operating the line switch C occurs when the calling subscriber pulls down the dial, whereby the rotary impulse spring 24 is momentarily pressed against the ground post 20. As a result, the trip magnet 47 of the line switch C is energized by a flow of current from ground Gr15 through the springs 18 and 19, ground post 20, rotary impulse' spring 24 to the rotary line conductor 32, conductor 185. 4), bridge-cut-off relay springs 186 and 187 to the trip magnet 47, thence through the said magnet to the conductor 188, differential relay springs 189 and 88, motor magnet springs 85 and 86, motor magnet 71 to the battery lead 190, thence through battery B to ground G. As soon as the trip magnet 47 energizes, the armature 51 is attracted and the plunger 44 is liberated and thrust into the terminal Q, by a spring 58. When the plunger 44 engages the bank terminal Q an energizing circuit is closed through the motor magnet relay 7 3, which in turn operates to close a circuit throughthe motor magnet 71. The motor magnet operates to place the idle plungers opposite the first idle bank terminal similar to the terminal Q. l The circuit through the relay 7 3 extends from ground G2 through the winding 191 of the relay 73, segment 74, wiper arm 7 5, contact 84, conductor 192, bank springs70 and 69, through the release magnet 48 to the battery lead 190, thence through battery B to the release magnet 48, the said magnet does not operatively energize, since the relay 73 is wound to a high resistance, while the release magnet is wound to va comparatively low resistance. The relay 73, upon energizing operates to close the springs 88 and 87 in contact, whereby a lcircuit is completed through the motor magnet 71 extending from ground G3 through the springs 87 4and 88, springs 85 and 86, motor magnet 71 to the battery lead 190, thence throughbattery B to ground G. The motor magnet 71, upon energizing, attracts its armature 81, wherel by the pawl 82. engages the ratchet wheel 72 and rotates the said wheel one step. vWhen the armature 81 is attracted against the magnet cores the springs- 85 and 86 disengage, thereby breaking the lenergizing circuit through the motor magnet. The cam-arm 76, being in engagement 'with the. pin 77, is operated to advance the plunger shaft 60, and lconsequently all idle plungers that may be in normal locked position, one step and opposite another bank terminal similar to the bank terminal Q; Also, the .wiper 75 is carried from the contactpoint 84, which corresponds to the terminal Q, tothe contact point 89, -which latter corresponds to the terminal before which the advanced idle plungers arenow resting. A

At the instant that the plunger 44 enters the bank terminal Q the following springs are. pressed into contact: 63 and 64, 65 and 66, 67 and 68, and 6 9 and 70. The engagement of the springs 67 and 68 establishes a circuit from ground G4 by way of the normal conductor 95 to the connector private bank contacts that correspond to the line that terminates in the line switch C, where by a guarding potential is established to prevent any subscriber from calling thel said line after the calling subscriber at substation A operates his dial preparatory to making a call, as explained. Theecircuit over which the lSaid guarding potential is established eXtends from ground Gt through the bank springs 68 and 67 to the private normal conductor 95, thence to the connector private bank. The engagement of the springs 67 and 68 also closes a circuit through the bridge-'cut-off relay 46 extending from ground G4 through the springs 68 and 67,

conductor 193,-through the relay 46 to thebattery lead 190,;thence through battery B to ground G. The said relay, upon energizf in breaks the contact between the springs 18 186 and 194, whereby the vertical and rotary line conductors 31 and 32 are dis-' connected from thetrip magnet 47. The closure of connection between the springs 69 and 70 establishes a guarding potential at g the master switch bank contact 84 over the following circuit.: `from battery B to the l 'battery lead 190, thence through the release magnet 48 and springs 69 and 70, conducpotentials.

tor 192 to the said contact point 84. It will be understood that the bank terminal Q, being the first bank terminal of the line switch bank, corresponds to the first seg ment 84 of the master switch bank O. This guarding potential protects the seized trunk conductors 90, 91 and 92 from being seized by other plungers.` Suppose that the master switch has operated and carried the wiper 75 to the last contact point 117. v Now, whenl the motor magnet 71 operates for the-next stepthat is, when another subscriber callsthe wiper 75 passes out ofl contact with the contact point 117 and into engagement` with pressed into contact, thereby closing an 'energizing circuit for the motor magnet 71 from ground G3 through the -said springs 87- and 88,` through the springs 85 and 86, motor magnet 71, thence to the' battery lead 190, and through battery B to ground G. The motor magnewthen operates, as previously explained, to rotate the ratchet wheel 72 one step for advancing the plunger shaft one step, and the master switchwiper 75 one step also, and into engagement with the second segment 89. When thus advanced one step the plunger` shaft 60 vcarries all idle plungers that are in locked engagement with the said plunger shaft opposite the next bank terminal, as Veq'alained. If there should be a guarding potential at the bank segment 89 of the master swihtchy bank the differential relay 73 will remain energized, whereby the energizing circuit through the motor magnet 71 is again comand 86 again engage; and as a result the motor magnetA 71 is again' operated, whereby the plunger shaft 60`and master switch wiper 75 are advanced another step. This operation continues as long as the wiper -pleted when the motor magnet lsprings 85 i 75 continues to find segments -with guarding As soon as an. idle segment is found, however, the energizing circuit through the differential relay 73 is broken, at which time the said relay in turn breaks the energizingcircuit. for the motor magnet 71 until the next subscriber makes a call. The closure of connection between the springs 63 and 64 extends the calling subscribers vertical conductor-31 to the, vertical trunk conductor `90, which latter leadspto the connector'vertical line relay 99. The closure of Contact between the springs 65 and 66 extends the subscribers rotary line conductor 32 tothe rotary trunk conductor 91, which latter leads to the connector rotary line relay 100.

The subscriber at substation A has thus established connection with the connector H, and now as the dial returns toward normal position, grounding the vertical' line conductor 31 each time that the impulse spring 23 is pressed onto the ground post 20, the vertical line .relay 99 of the connector H is energized by a flow of current from the sub* station ground G15, and immediately before the dial stops the impulse to the rotary line conductor 32 energizes the connectoi rotary line relay 100 also. The circuit through the vertical line relay 99 extends from ground G15 through the springs 18 and 19 to the ground post 20, thence through the impulse spring 23 to the vertical line. conductor 31,v

line switch bank springs 63 .and 64, vertical trunk line conductor 90, vertical line relay 99 to the battery'lead 190, thence through battery B to ground G. Each time that the vertical line relay 99 energizes, the relay spring 196 is pressed onto the ground spring 197. The vertical magnet is thereby energized, and the wipers 96, 97 and 98 of the connector are raised one step at a time to the tenth bank level and brought opposite the first contact of the said level. The energizing circuit of the said magnet extends from ground G5 through the springs 197 and 196 tothe conductor 198,.switching relay springs 199 and 200, private magnet springs 201 and 202, side switch wiper 107, contact point 203, through the vertical magnet 101, thence to battery lead 190, and through battery B to ground G. On the tenth step the arm 204 upon the end of the shaft presses Athe springs 123 and 124 into engagement.

As previously explained, when the shaft is raised to t-he tenth level the connector acquires the rotary or automatic selective feature of the selector. Therefore, when the rotary impulse energizes the rotary line relay 100, and as a result the private magnet is in turn energized to cause the side switch to pass to second position, the connector shaft is automatically rotated. YThe energizing circuit throughtheline relay extends from ground G15through the springs 18 and 19, ground post 20, rotary impulse spring 24 to the rotary line conductor 32, line switch bank springs 65 and 66', trunk conductor 91, rotary line relay 100 to the battery lead 190, thence through battery B to ground G. vThe rotary line relay, upon energizing, opera-tes to place the springs 207 and 197 in contact, whereby an energizing circuit is closed through the private magnet 103. This circuit .extends from ground G5 through the springs ,197 and 207,' switching relay springs 208 and 209, then through the into contact, and the side switch passes to to the trunk-line is busy the shaft is automatically rotated onto the next set of contacts; also, if the second set of contacts leading to the main exchange is busy the connector shaft wipers are rotated tothe next trunk line. This automatic rotation is brought about as follows On-the tenth vertical impulse, when the normal arm 204 presses the springs 123 and 124 into contact, an energizing circuit is established through the relay' 125 which, upon energizing, operates to press the springs. 211 and 212 into -contact and to carrythepspring 213 from the sp-ring v214 to the spring 215, whereby a new energizing circuit is established throu h the private magnet 103, said circuit exten ing from the grounded private bank contact 210 to the shaft vwiper 98, side switch wiper 108, contact point 216, through the springs 213 and 215, then through the winding of the private magnet 103, and through battery B to ground G.

When the springs 211 and 212`are pressed second position, an energizing circuit is closed through the rotary magnet 102, extending from' ground G5 through the interrupter 126, springs 211 and 212, contact point 217, side switch wiper 109, through the rotaryv magnet 102 to the battery lead 190, thence through battery B to ground G.

vThe rotary magnet operates to carry the shaft-wipers 96, 97 and 98 onto the iirst set of contacts of the tenth level, and when the shaft wiper 98 engages the grounded contact point 210 the said private magnet is maintained energized, and the side switch isretained in second 'position as long as the wiper 98 engages a busy or grounded con- 115 tact. This energizing circuit through the rotary magnet 102 is maintained, and when an idle contact is found the energizing cir` cuit through the private magnet becomesbroken and the side switch passes to third position, whereby the energizing circuit through the rotary magnet becomes broken when the side switch wiper 109 leaves the contact point 217. If the first and second sets of contacts` allotted to the 'trunk-lines 125 arebusy, the energizing circuit through the private magnet is maintained until the private wiper is rotated onto the insulated contact, when the private magnet is released.

The side switch is thus tripped to third po- 130 I sition, the rotary magnet circuit .broken and .the calling subscriber connected to the busy signaling current. If the first set of con tacts allotted to the trunk-lines is not in use, there is no guarding potential at the nri- V vate wiper 98 to lock and hold the private magnet when the rotary impulse begins, and therefore the side switch passes to third position. At the instant that the side switch passes to thirdy position, the connector side switch wipers 105 and 106 having engaged the contact points 218 and 219, the calling subscribers line conductors are extended into connection with the normal conductors 220 and 221, which latter lead to the line switch C2 allotted to the trunk-line conductors 222 and 223. Furthermore, when the side switch passes to third position a guarding potential is established for protecting the-called line. This guarding potential extends from ground G7 to the contact point 224, side switch wiper 108, and shaft wiper 98, which latter engages the private contact Aof the called trunk-line. vThe energizing circuit through the cut-off relay 225 extends from ground G7 to the private wiper 98, as eX plained, through the conductor 226, cut-oli' relay 225 tothe battery lead 190, thence.

' through battery B to ground G. The said relay, upon energizing, 'operates to separate the springs shown in contact in F ig. 1, and to carry the spring 227 into engagement with the spring 228, whereby the'vertcal tical trunk-line conductor 222.

normal conductor 220 is extended to the ver` Furthermore, when the side switch wiper 109 passes to' third position an energizing circuit is closed through the switching relay 113. This circuit extends from ground through the normal springs 123-and 124, Winding of the switching relay 113, side switch wiper 109, through the Winding of the rotary magnet 102 to the battery lead 190,- thence through I battery B to ground G. Although this circuit includes the rotary magnet 102 the said magnet does not operatively energize, since 'the relay 113 is wound to a high resistance,

` 102 is comparatively low. The relay 113,

while the resistance of the rotary magnet upon energizing, operates to shift the springs 19.9and208 -from the springs 200 and209 to the springs 229 and'230, whereby the vertical and rotary .line relayA springs 196 and 207 are connected with the shaft.. wipers -96and 97, respectively Hence, when the connector vertical androtaryline' relays 99 'and 100 are energized, the said relays operate to deliver or repeat impulses tothe line conductors engaged. bythe shaft Wipers4 96 and 97. The subscribers line conductors 31 and 32 being thus ex'tended to the trunkllineconductors 222:V and" 223, respectively,

which terminate in the first-selector switch E of the main or central exchange the subscriber at -s'ubstationA is now'ready to call -228 and 227 of the line switch C2 is without effect at this particular time.

The preliminary impulse .is effective only when the rdial is turned the first time. The first digit being 2 the subscriber at substation A operates the dial accordingly, and the spring 23 is thereby pressed onto 'the ground post twice. As a result, the ver-4 tical line relay of the connector H is energized twice by a flow of current from ground G15, as previously traced. The connector vertical line relay, upon energizing, operates to press the springs 197 and 196 into contact, whereby the ground impulses are repeated to the vertical trunk conductor 222 for energizing the vertical line relay 142 ofthe firstselector E. This energizing circuit extends from ground G5 through the connector vrelay springs 197 and- 196, conductor 198, switching relay springs 199 and 229, side switch Wiper 105, shaft wiper 96 to the normal conductor 220, cut-oil'. relay springs to the vertical tr11nk-lineconductor 222, through the side switch Wiper 131, contact point 231 line relay 142 energizes, the line relay spring 145 is pressed onto the ground spring 144'..

The .vertical =magnet 127 is thereby energized and the wipers 138, 139 and 140-of-theselector E are raised to the -second bank leve-l and brought opposite the first contact of i said level. The energizing circuit for the said vertical magnet 127 extends. from ground GB through the springs '144 and 145,

private springs and v136, 'and through the vertical magnet 127 to battery B andto ground G.' Following the vertical iinpulses, Itherotary impulse spring24 is then pressedonto thel groundpost 20,' grounding 'the rotary line conductor 32 and energizing,

therefore, the rotary 'lin-e relay 100 'of the 'I i.

connector .H over a circuit previously traced.

The rotary line'relay 100' of the connector 1in-turn operates tojplace the springs 207 and 197 in contact, whereby.. the impulse is repeated to the rotary trunk-l'ne conductor 223,` and then to the first-seector rotary line rela 143, over a circuit extending from .ground 5 through the 'springsl197 and 207,-

magnet 128 .to the battery ELO switching relay springs 208 and 230, side switch wiper 106, shaft wiper 97, conductor 221, rotary trunk-line conductor 223, side switch wiper '132, Contact point 234, rotary line relay 143, through the springsvof the cut-off relay 232 to the battery lead 233, thence through battery B toground Gr. The rotary line relay, upon energizing, presses the line relay spring 146 onto the ground spring 144, thereby establishing a circuit through the p-rivate magnet 129 from ground VGr8 through the springs 1.44 and 146 to the private magnet 129, and through the said magnet to battery lead233, thence through battery B to ground Gr. The private magnet, upon energizing and de-nergizing, permits the` selector side switch to pass from first tosecond position, permitting the Side Switch wipers 133 and 134 to engage the contact points 235 and 236, respectively.

The closure of connection between the Side switch wiper133 and the contact point 235 sets up an energizing circuit for the rotary magnet 128 from ground G? to the contact point 235, through the side switch Wiper 133, interrupter springs 141, rotary lead 233, and then through battery B to ground Gs. The said rotary magnet 128 then operates to rotate the wipers 138, 139 and 140 of the selector E into en agenient, wit `h the .first trunk-terminal oi t e second level of the selector E, from which terminal, it isassumed, the

- trunk-line conductors 237, 238 and 158 lead i 1 locking the side The energizing circuit for said private mag! -.net extends from to the second-selector4 F. If the 4first trunk is busy, however, contact will be found grounded, andothen as soon as the private wiper 140' engages the first grounded private bank contact point, the private magnet 129 fenergizes again, switch in second 'position.

the grounded terminal of battery -B through. an occupying switch (not shown) to the private wiper 140, thence through the back-release relay 147 -to the side switch wiper 134, contact point 236,-prionly the first,

6o thatthe private. wiper .leaves vate magnet 129,

tery .B to ground G. \The private magnet becoming energized, locks the side` switch the step are carried beyond if, for example, not but also the second, or .still At the instant the last busy contact point, the'energizing circuit through last busy trunk-hue,

other trunk-lines are busy.

the private magnet 129 4is destroyed, and as a result theI selectorthird position.

vside switch'passes to If, however, there4 are no busy trunk-lines,

.lead to the selector switch F.

the first private bank .thence through said-mag- 5' net to the battery lead 233, and through bat-- o. 129, upon thus wiper .133 in engagement .with the contact point 235, whereb 4 rotary magnet 128 will be energi'zec7 bfy' stepuntil the Wipers meets thefground post 20..

the rotary magnet' 128 re-v leases the side switch to third'positionas r Corr soon as the wipers are carried into engagement with the first trunk-line. As soon as the side switch passes to third position, as stated, the subscribers line conductors 31 and 32 are extended to the conductors 237 and 238 which, in this case, it is assumed i The extension 'of the line occurs, of course, as soon as the side switch wipers 131 and 132 engage the contact points 240 and 241, respectively. Not only is the subscribers line thus extended, but a guarding potential is, established at the private wiper 140, when the side switch wiper 134 passes onto the ground contact point 242, for protecting the seized trunk-line from interference by other calling subscribers. This guarding potential is established from ground G1 to the contact point 242, thence through the side switch wiper 134 and through the back release relay 147 to the private wiper 140. Furthermore, when the Selector shaft is given the first vertical step the vnormal arm 243 permits the springs 244 and 245 to engage, whereby an energizing circuit is established through the relay 184 of the repeater J, which relay in turn oierates to establish a guarding potential at t e secondselector banktopro'tect the repeater J from being seized by a secondselector, thus preventing any subscriber from calling out on the trunk-line conductors 222 and 223, through the repeater J, while the said conductors are being' used -by an incoming'call. The circuit through the relay 184 extends from ground Grl1 vthrough the springs 245 and 244, conductor=246, springs 247 and 248, through the winding of the relay 184- guarding potential at the second-selector private banks extending from ground UP` through the springs 249 and 250, conductor `2.51thence'to the private bank contact 252, thus protecting theseizure at the main central exchange while seizedA at the sub-central exchan f', as explained.

'It will be seen, of course, that the energizing circuit for the rotary magnet 128- (to -which reference has already been made) is destroyed when the idle trunk-line is seized-that is, when the side switch wiper 133'leaves the Contact point 235. The second digit of the number called being 2, the callingsubscriber again operates his dial accordingly, as a result grounding the vertical line conductor 31 when the spring ,23 'Since the 'line conductors 31 and 32 have been extended to the conductors237 and 238 (Fig. 2) which leadto the selectonF, the vertical and rotary line relays ofthe connector H, upor() trunkline against energizing for the second digit, operate to repeat the second digit impulses to the selector switch F in the same manner as the first digit'impulses were repeated to the selector switch E. The vertical line relay 148 of the selector F is, therefore, energized twice by a lflow of current from ground G at the connector H to the vertical trunk-line conductor 222, as explained, thence to the side switch wiper 231 of the selector E, conp and lnaughtare eifectivh tact point '240, vertical line shaft wiper 138, vertical trunk conductor 237, side switch wiper 150, contact point 253, verticalline relay 148 to the battery lead 233, thence through battery B to ground G-that is, when the vertical line conductor 31 is grounded lfor the second digit the Vertical line relay 148 operates to close a circuit through the vertical magnet 152, which in turn operates to carry the shaft wipers along step by step and bring them opposite the bank terminals of the second level, as eX- lained invconnection' with the selector E.

hen the rotary line conductor 32 is grounded after the vertical impulses, the rotary line relay 149 of the second-selector -F is then, in'order, energized by the repeatedimpulse from the connector H, whereby an energizing circuit is in turn es- `tablished through the private magnet 155,

which private magnet then operates to release the side switch of the selector F, as described in connection with the selector E. This selector then performs the usual trunk-selecting operation, as before described in connectionwith selector E; and

after the switch F comes to rest the shaftv wipers 159 and 160 will be found in engage-` ment with thetrunk conductors 254 and 255, respectivel which lead to 'the connec tor switch-I. gt the same time the private wiper 161 establishes a protecting potential lat the private contact 256 for guarding the `seized trunk-line. AWhen the side switch wipers V1.50and151 engage the contact points and 258 the calling subscribers line con'- ductors 31 and 32 are still farther extended to the connector switch, I.- The groundimpulses from the substation 'to the line-conductors for the last two digits, namely two in operating thev connector lI. For the third digit- 2 the ver-l ticalimpulsespring 23 is pressed onto the.

ground post 2() twice, :whereby an energizing circuit is each time closed through the connector vertical line relay '165. The impulses arc each time repeated by the vertical line relay of the connector H to the vertical line relay of the connector I, in l.the

same-manner in whichthe imlpulses are repeated to the selectorsE and Eachtime that the -vertical line relay 165 ofi the connector- I is energized the line relay springslv "259-and 260 are pressed into contact, there* by closing-'an energizing circuiteach time through. the vertical magnet 167, which latter operates in the usual manner, one ste at a time. The shaft wipers 162 and 163 are, therefore, raised two steps and brought opposite the level in which are located the terminals of the normal conductors 261, 262 and 263 that lead to the lirst-selector switch E2 allotted to the line of the called substation. The normal conductors 261 and 262,

however, are connected with the line conductors 264 and 265 which'lead to the substation Aa. After the connector shaft has been raised by the vertical impulses the rotary impulse is sent'in. This is done whenthe rotary impulse spring 24 makes contact with the ground post 20, thereby closing an energizing circuit through the rotary line relay 100 of the connector H, and the impulse is in turn repeated to the rotary line relay 166 of the connector I.

The rotary line relay 166, upon energizing, closes an energizing circuit through the private magnet 169, which in turn operates to release the connector side switch from first to second position. The last digit being naught, the calling device is operated as previously described, grounding the vertical conductor 31 ten times and the rotary line conductor 32 once. The vertical and rotary line relays 165 and 166 are operated. as before. However, When the line relay springs259 and 260 engage, a circuit is closed' through the rotary magnet, 168, instead of through the vertical magnet 167. Each time that the rotary magnet is energized it operates to rotate the shaft and shaft wipers 162, 1 63 and 164 one step at a time until the said wipers are carried into engagement with the conductors 261, 262 and 263 which are allotted to the line of substation A3. The energizing ofthe rocompletes an energizing circuit through the private magnet 169, which now operates..

with one of two results, namely the release -Of the side switch from second to third position thus placing the. side switch .wipers 171, 172, 173 and. 174 in contact with their respective contact points of the third position, or the .so-called busy-release of the connector. It will first beassumed that the first result occursthat is, that the side switch passes to third position. When the side switch Wiper 174 engages thel contact point 266 a ground potential is established at the connector bank, The saidguarding potential. also provides an energizing circuit for the bridge-cut-o' relay 267 of the first-selector E2, thereby removing lthe bridge formed by the vertical and .rotary line relays of thefirst-selector E2. f

-To signal the called-subscriber the .calling subscriber. presses the lsignaling button -37, placing the lspring v35 in, contact with the substation ground G1, thereby energizing line relay 165 when the vertical line relay 99 of the lconnector H, and in turn the vertical line relay 165 of the connector l. The path of the energiz- .ing circuit for the relay 99 of the connector H extendsv from ground G15 through the springs 18 and 19 to the contact point 38, spring 37, springs 33 and 34 to the vertical line conducto-r 31, trunk conductor 90, vertical relay 99 -to the battery lead 1.90, thence through battery B to ground Gr. This relay, upon energizing, repeats the impulse t) the vertical .line relay 165 of the connector I.`

It will be remembered that the connector side switch 'has passed to third position, and that the side switchwiper 173 is in engagement with the contact point 268, thereby placing the vertical line relay-y 165 in control of. the ringer relay 177 in the` same manner in which the rotary magnet 168 came under the control of the vertical the side switch passed 'rom first to second position. Therefore,

nector shaft wiper when the vertical line relay 165 presses the springs 259 and 260 into contact the ringer relay 177 is energized by a flow. of current from 260, through the private magnet springs, side switch wiper 173, contact point 268 to the ringer relay 177 and to the battery lead 233, thence to battery B to ground G'. The ringer relay, upon energizing, shifts -the springs 269 and 270 from the springs 271 and 2 72, respectively, and onto the ysprings 273 and 274, respectively. This results in separating the calling subscribers Iline from the called subscribers Iline, and

in bridging across the line of :the latter the terminals of the ringer generator. M. A signaling current is, the generator M to the ringer 'relaysprings 273 and 269, side switch wiper 172, contor 262, line conductor 265., condenser 275, ringer 276, spring 4277, switch-hook 278 to the vertical line conductor 264, normal conduct-or 261, connector shaft 'wiper' 162, side 1 v switch wiper 171, ringer relay springs 269 and '270 resume.

springs 270 and 274 back to the generator M.

As soon as the calling subscriber ceases.

.to press the signaling button 37 the ringer relay 177 becomes secondary springs 282 an 'd 283.- The local transmitter.. circuit is' closed as soon as the springs 284 and 285 engage in contact.` The A two substatons A and As over the circuit shown are now connected by heavy `lines 1n ground to the relay springs 259 and,l

therefore, sent from 163, normal conduc-v Aaremoves the receiver Figs. 1, 2 and 3, namely: The conductors '264 and 265 of the called. line, the normal conductors 261 and 262, comlensers 364 and 365, 'wipers 159 and 160, side switch wipers 15() and 151, conductors 237 and 238, wip-- ers 138 and 1.39, side switch wipers 131 and 132, trunk conductors 222 and 223, con ductors 220 and 221, wipers 96 and 97 of the connector ll, side switch wipersand 106, condensers `and 111, conductors 90 and 91, bank springs 64 and 63 on one side and 66 and 65 on the other', and. the conductors 31 and 32 of the calling line. TheI release of the central office switching apparatus occurs when theV calling subscriber restores the receiver 2 to the switch-hook 3,

thereby pressing the release springs 7, 8 and 9 into engagement for amoment. Thel contact of the said release springs grounds the vertical and rotary line conductors 31 and 32 simultaneously from ground G15 to the vrelease spring 7, thence through the springs 8 and 9 to the vertical and rotary line conductors, thereby simultaneously energizing the vertical and rotary line relays 99 and 10Q of the connector H, which relays operate to in turn ground the trunk-line conductors 222 and 223, whereby the vertical and rotary line relays and 166 of the connector are energized simultaneously, thereby placing. the trunk-release springs 286 and 287 in contact and thus closing an energizing cir- Vcuit including the'release relay 288 of the second-selector F in series with the release magnet of the connector I. The path of the circuit extends from ground G13 to the side switch wiper 289, release -relay 288, se-

lector shaft wiper 161, connector trunk-release springs 286 and 287, release magnet 170 to the battery lead 233, thence through battery B toV ground. G'. When the-connector release magnet 17 O is thus supplied with eurrent it energizes', and as a result the switch shaft andside switch are restored to normal position, thus. breaking the connection between t'he connector switch shaft wipers '162,

163and 164 and the normal conductors 261,

' 262 and 263, and,.therefore, breaking the energizing circuits 'of the bridge-cut-o' relay 267 of the selector E2. The back-release relay 2,88 of the second-selector F, being' in the same circuit with the release magnet 170, energizes simultaneously with the latter, and presses the springs 290 and 291 into engage- 'Inent which in turn close an energizing circuit through the release relay 147 of the firstselector E in series with the release magnet 154 of the second-selector F. This circuit extends from ground G1,lsid e switch wiper 134, through therelease relay 147, shaft Wiper 140, springs 290 andp291, through the winding of the release magnet 154 to the battery lead 233 thence through battery B to ground G. The release relay 147 energizes, and places the springs 292 and 293m in contact, whereby an energizing circuit is closed through the release magnet 104, which latter then operates to close a circuit through the release magnet 48 of the line switch (l, said circuit extending from ground through the springs 295"L and 296, conductor 92, bank springs 70 and 69, through the winding of the release magnet 48 to the battery lead 190, thence through battery B to ground G. All of the relays and magnets thus energized I attract theirrespective armatures and remain energized until the substation release springs 7, 8 and 9 separate and break the ground connection with the line conductors 31 and 32, at which time they all denergize,

and the remaining unreleased switches are restored. The calling subscriber thus rei speak, while this energized.

' stores all switching apapratus which he originally brought into use. It will be evident that if the calling subscriber neglects to release the switches the called subscriber (F ig. 3) is unable to operate his switch E2 as long as the connectonswitch I remains connected 'to the line #2220, on' account of the lcut-,off relay 267 being energized. AThe back-release is provided in order Athat called subscribers may vnot remain helplessly tied up, so to bridge-cut-off relay 267 is Should the called subscriber desire to make an independent call before the calling subscriber releases he may do so by first l breaking the established connection and thus `securing control of the first-selector E2.

After, establishing connection. between the' ground springs 296 and 297 he ma ground the line conductors 264 and 265 simultaneously by restoring the'receiver- 279 ,to the switch-hook 278, and thus 'pressing' the re- .jlease springs 298, 299 and 300 into enwil pass throughrelay 175 andt Ast ga ement. As a result an-energizing circuit the .vertical back-bridge 176 ofthe connector I. The circuit 'through the vertical back-bridge relay `extends fromthe lsubstation ground G1* to the ground springs 296 and 297, to the springs 298 and 299, vertical conductor 264, normal conductor 261, shaft wiper 162, side switch wiper 171, lringer relay springs 270 and 272, vertical back-bridge relay 175 tol the'battery lead 233, thence through :battery B- to ground G. rllhe energizingcircuit of the rotaryiback-bridge relay 176 extends from ground G14, to therelease springs298, 299 'and 300, to the rotaryline conductor' `265,

normal conductor 262, shaft wiper 163, side switch wiper 172, ringer relay springs 269 and 271 and rotary back-bridge relay 176 to the battery lead 233, thence throu h battery B to ground G. The back-bridge relays 17 5 and' 176, upon energizing simultaneously, press the back-release springs 301 and 302 into contact which completes an energizing circuit to the release magnet 170 from ground to the springs 301 and 302, through the release magnet 170, battery lead 233 thence through battery B to ground The release magnet is energized and the switch shaft wipers 162, 163 and 164 and side switch are restored to normal position. The ener izing circuit through -the bridge-cut-o relay 267 is broken when the shaft wiper 164 'leaves the private bank contact. The connector switch I. is thus released and the first-selector E2 is restored to the control of the substation #2220lQBy grounding the line conductors 31 and 32 the subscriber A may restore the remaining switches.

In the .preceding it has been explained that when the last rotary impulse comes in the connector switch is liable to be released, or the side switch may pass to the third position, depending upon the condition of the circuits. It was rst assumed that the side switch had passed to third position, and the explanation was made accordingly. It will now be assumed that the called line isbu'sy for any reason whatever and, therefore, that the private bank contact allotted to the line #2220 is grounded'. This being the case, it will be explained how the'busy-release of the conductor follows at the instant that the rotary line relay 166;y is energized bythe 166, jupon energizing, energizes the private magnet 169, as ,previously described, which llatter in turn presses the springs 303 and 304" into contact. -Assoon as the said .1m

springs 303 and 304 engage', the release magnet 170 is placed in connection'with the prlvate wiper 164 (since the side switch wiper 174 is now in second position), which wiper y164 has been 'previously rotated onto a grounded contact. .As a result, a flow of current is sent through'the -releasemagnete rotary back-bridge relay 4170- from the grounded vprivate, wiper -164 to 'the sideV switch-wiper .174, through'the private magnet springs 303 and 304, to the;

stores the connector4` side switch toits firstl l position, retunin the vertical' magnet 167 to the control o the Avertical relay 165.

Therefore, if the calling subscriber (Fig.

1) presses the signaling buttonj 37 and grounds the vertical line conductor- 31, he

' operates the vertical "line relay 16,5, which latter in turn operates the vertical magnet 167. The vertical magnet armature raises the switch shaft so that the normal post arm 305 permits the switch shaft spring 306 to come into contact with the contact 307, and the busy-signaling current is sent from the busy-signaling machine N to the calling subscribers station. Upon hearing the busy-signal the callingsubscriber will understand that the desired line is in service and will release the switching apparatus, over the same circuits previously described, by hanging up his receiver.

It will be understood, of course, that the ground at the private bank contact that causes the busy-release of the connector is due to the fact that the called line may be either calling or has beencalled. In the former case the round connection is closed by the selector 2, to the extent that the shaft, upon rising, permits the shaft springs 366 and 367 to come into contact. In the latter case-that is, if the-called subscriber has been called-the ground is supplied by the connector that has made the call in the same manner that has already been explained in connection with the connector I.

The explanation that has preceded in ref erence to the call between the subscriber- A (Fig. l) and the subscriber A3 (Fig.- 3) refers to a case, as h as already been stated, when a subscriber of the exchange indicated in Fig. 1 calls the subscriber of the exchange indicated in Fig. 2, as, for example,

where the subscriber A is the subscriber of a private branch exchange' and the subscriber A3 is a subscriber of the main exchange, the two exchanges being connected by suitable trunk-lines which, in this case, as has been explained, lead of from the tenth level of the connector switch H. It has already been explained that if any subscriber of the private branch sub-exchange (Fig. 1) wishes to call any other subscriber of the same exchange, he may do so by using the connector H, which connector 1n that case picks out the desired line in some level other than the tenth level, This specific 'arrangement, however, it will be seen, is not esesntial.. To illustrate: When the subscriber at substation A calls a subscriber of the same local sub-centralexchan e as theA subscriber at substation A on the ine #20,

for example, the connector H operates in the usual mannerthatis, the subscriber controls both the vertical and rota movements of the switch shaft. To call ltlie number 20 the subscriber at substation A turns the dial for the first digit 2, whereby the trip magnet 47 of the line switch` C is, energized and operated, aspreviously explained,

Yto seize an idle trunk-line leading to a con'- nector switch H. 0n the returnlmotion of the dial the vertical line conductor 31 is grounded twice, :thus energizing the vertical line relay-99 twice oyercircuits already shown. The vertical line relay 1n turn closes an energizing circuit through the verdigit naught, an energizing circuit is closed through the rotary magnet 102 extending from ground G5 through the springs 197 and 196, switching relay springs` 199 and 200, private magnet springs 201 and 202, side switch wiper 107, contact point 309, and

through the magnet 102 to-the battery lead' f 190, thence through battery B to ground G.

times, the rotary magnet is in turn energized ten times, and the shaft wipers 96, 97

and .98 are carried into engagement with the bank contacts that constitute the ter- .-minals of the line #20. When the private magnet 103 is energized by the rotary line relay 100 for the last digit, one of two results occurs, namely' the release of the side switch from second to third position, or the so-called busy-release of the connector switch if the desired line is busy. 1t will be assumed that the first result occurs-that ais, that the side switch passes to third'position. As a result, the side switch wiper 108 eig-gages the contact point 224,.:1. guardingpotential is established at the connector b-ank to protect the called line, and an energizing circuit is closed through the cut-ofil relay 310 of the line switch 'C'. p from ground Gr. through the side' switch wiper 108 t'o the shaft wiper 98, conductor l311, thro-ugh they cut-ofi' relay-310 to the battery lead, 190, thence through battery B to round G. The cut-'off relay, upon energizing, places the springs 312 and 3 13 in contact, whereby the vertical'normal conductor 314 is connected with the vertical line con ductor 368. The rotary line conductor 315 is connected with the ;rotary' normal conductor 316. n l

scriber at substationA presses the signaling button 37, whereby thel vertical. line relay 99 isl again energized. Since4 the side. switch springs 197 and 196, switchingrelay springs 199. and 200,'private magnet springs 201 and This` circuit extends" The vertical relay 99 being energized ten' 202, side switch wiper 107,-contact point 317, through the ringer relay'112 to the' battery lead 190, thence through b-attery B to ground G. The ringer relay, upon energizing, operates, as explained.- in connection with the ringer relay of the connector I, to bridge t'he ringer generatrn.l K across the terminals of the called line for operating the substation ringe-r 318. The subscriber at substation A', in response to the signal, re moves the receiver from the switclrhoolr. The two substations A and A being connected over the circuit shown by heavy line conductors in Fig. l, conversation may be carried on. The release of the connector and line switches is brought about when the calling subscriber restores the receiver 2 to the switch-hook 3, thus grounding both line conductors 31 and 32 simultaneously and energizing the vertical and rotary line relays 99 and 100, whereby the release mag net 104 becomes energized and, as pointed out, operates to close a circuit through the release magnet 48 of the line switch C. The release magnets 48 and 104, upon energizing, attract their respective armatures and remain in readiness to resto-re their respective switches when the release springs 7, 8 and 9 disengage, thereby removing the ground from the line conductors 31 and 32. The so-called busy-releaseof the connector follows as a result of energizing the private magnet for thev last digit when' the called line is busy. If the called line is busy the private Wiper 98 rests on a grounded-or protected contact. magnet 103 is energized for the last digit the lground potential `at the shaft Wiper is transmitted to the release magnet 104 over a circuit extending from the Wiper 98 to the side switch Wiper 108, contact point 2116 bearing in mind that the side switch is 1n second position), through the springs 213 -and 214 to theprivate magnet spring 819 and'to the spring 320, upon the energize.-

a relay tion of the private magnet, then through the release magnet 104 to the battery lead 190,- thence through battery B to ground G.

The release magnet 104, upon energizing, operates to close the springs 295EL and 296a in contact, whereby. an energizing circuit is closed throu h the release magnet 48 of the line switch Thus the release of both the connector H and the line switch C is-brought about when the connector calls in on a busy line. Thinking that connection has been establ'ished the subscriber presses the signal-v ing `button 3 7, thus lgrounding the vertical line conductor 31, whereby an energizingcircuit is completed through the-trip magnet 47 of the line switch C fromtheconduc'tor :31, through thesprings 194, 186 andf187, winding of the trip magnet 47, differential springs 1'89 and 88,*through the wind,- ing of the motor magnet 71 to the' battery lead 190,'thence through battery B. to ground G, .The trip -magnet, uponenergizing, op-

Now, when the private .exchange (Fig. l).

- change; but when a erates as before to seize an idle trunk-line leading to a connector switch. As soon as the line switch operates, the springs 63 and 64 engage7 thereby extending the ground connection of the vertical line conductor 31 to the trunk conductor 90, and then through the connector vertical line relay 99 which operates to close a circuit through the vertical magnet 101. The connector shaft is raised one step and the normal arm 204 permits the springs 121 and 122 to engage, thus connecting the busysgnaling machine L with thev side switch wiper 106 which 'Es now in rst position. Upon hearing the busy-signal the calling subscriber will understand that the desired line is busy and lwill restore the switching apparatus by hanging up the receiver.

It has been shown how'the subscriber at substation A may call andsignal the subscriber A3 also how the subscriber at substation A call and signal a subscriber of the same or sub-exchange. It will be pointed out how a subscriber of the main central exchange may call and signal a subscriber of the sub-central exchange (Fig. 1).' As

may local "shown in Fig. 2, it will be seen that the conductors-333 and 334 leading to. the repeater J lead off from the fifth level of the secondselector banks, and Vthat the conductors 343 and 344 leading from the repeater are connected in multiple withthe first-selector E tothe same trunk-line, vvhichtrunk-line terminates in the pri-vate branch or.sub-central It will be evident that 'from the said fifth level of the second-selectors ten repeaters J may be reached, and, therefore, ten different. trunk-lines to the eX- change4 shown in Fig. 1. As explained,the rst-selector is used the main exchange4 from the'sub-c trai ex-v call goes vfrom the main exchange to the sub-central the 'repeater J is called into service instead. When the reof the main central exchange, and "i when a call i made into 'i at the exchange shown in Fig. 1 from the main exchange, the prex 35 must be given to every number-'of said exchange'. For example: Assume that the subscriber at sub.- station A2 of the main .exchange (Fig. 2) desires to call the subscriber at substation A (Fig. 1).,.tl1`e number of'which is20, as already stated. In that event. the subscriber at substation A2 must'flrst turnhis dial for the digit 3,- Whereby the firstselector E may be operated 'to raise its shaft Wipers. to the-l vthird level, and

When in said level rotated 

